Device and method for monitoring rooms equipped with high-voltage apparatuses

A monitoring device for determining the concentration of a dielectric insulation fluid such as a perfluoroketones in a room housing at least one high-voltage electrical apparatus and being accessible by humans essentially without modifying the room conditions, for example the room being a part of an air-insulated substation, with the monitoring system including one or more sensors for determining an emission and/or absorption of the dielectric insulation fluid molecules at at least one wavelength or wavelength band of the electromagnetic wave spectrum.